Strange landline fault - dial tone disappears until incoming call

Werdnal

Mum in Law has intermittent problem with her landline. Dial tone keeps disappearing, meaning she cannot make calls. Incoming calls work OK, and after a successful call received, dial tone comes back, but will then randomly disappear again some time later. This is concerning for us as she lives alone and has a lifeline pendant alarm, which works through phone line so needs to be 100% available.

We disconnected all extensions this morning, and plugged a known working handset into main incoming box. Initially no dial tone, but when I rang number from mobile, call rang, answered and connected OK. Then after this, dial tone was present and calls could be made again. This is at least the 3rd time this has happened in recent weeks, and as dial tone eventually returned on previous occasions, she didn't tell us as thought it may be BT working on system that had disconnected her. She didn't note coincidence of incoming call triggering the dial tone to come back.

Rang her phone provider, who went through some tests which showed line was fine and suggested its her internal phone. I wanted to log for engineer check but got the usual "it will be £100 call out if not wiring problem", so reluctant to sting her with a bill. Any suggestions what might be causing this or come across similar before we resort to fault log please?

Browntoa

Bad joint outside somewhere , possible water ingress

I've got an intermittent broadband fault , line always passes the test but it's definitely line fault as both me and my neighbour get the same thing

Owain_Moneysaver

It's an established fault pattern. The higher ac ringing voltage is sufficient to break down any dampness causing a short on the line and the line will be usable for a short time afterwards.

Werdnal

Thanks both.

The "short" on line makes sense, and incoming call breaking the resistance enough to reconnect it is logical to me. Pity the operator I spoke to when I tried to report earlier had never come across this before ... he insisted it must be her phone! Wouldn't accept a fault log from me either as I am not account holder, so going down tomorrow to call them again with her sitting next to me to confirm I have permission to act on her behalf.

I only hope whoever visits understands, as she won't be able to explain it to them and sods law will say its not showing any fault on test! Do Openreach Techs have more thorough test equipment than the remote line testing? Is there a specific term for the fault ... we had a "ring trip" a few times, and once I knew what it was called, it was easy to explain to the guy who came out each time.

Thanks again for replies